Path Computation Element communication Protocol extension for relationship between LSPs and Attributes
draft-dhody-pce-association-attr-01

Abstract

The Path Computation Element (PCE) provides functions of path computation in support of traffic engineering in networks controlled by Multi-Protocol Label Switching (MPLS) and Generalized MPLS (GMPLS).

This document defines a mechanism to create associations between a set of LSPs and a set of attributes (such as configuration parameters, policy or behaviors).

Status of This Memo

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This Internet-Draft will expire on January 22, 2015.

Copyright Notice

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Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Terminology
• 3. Motivation
• 3.1. Opaque Identifier
• 3.2. Policy based Constraints
• 3.3. Bundled requests
• 4. Overview
• 5. Attribute Association Group
• 5.1. ATTRIBUTE-OBJECT-TLV
• 6. Security Considerations
• 7. IANA Considerations
• 8. Acknowledgments
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Appendix A. Contributor Addresses

1. Introduction

[RFC5440] describes the Path Computation Element communication Protocol (PCEP) which enables the communication between a Path Computation Client (PCC) and a Path Control Element (PCE), or between two PCEs based on the PCE architecture [RFC4655].

[I-D.minei-pce-association-group] introduces a generic mechanism to create a grouping of LSPs which can then be used to define associations between a set of LSPs and a set of attributes (such as configuration parameters or behaviors).

This document specifies a PCEP extension to associate one or more LSPs with a set of attributes, which includes, but not limited to -

• Configured Parameters
• Policies
• Behaviour

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

2. Terminology

The following terminology is used in this document.

AGID:

Association Group ID.

LSR:

Label Switch Router.

MPLS:

Multiprotocol Label Switching.

PCC:

Path Computation Client. Any client application requesting a path computation to be performed by a Path Computation Element.

PCE:

Path Computation Element. An entity (component, application, or network node) that is capable of computing a network path or route based on a network graph and applying computational constraints.

PCEP:

Path Computation Element Communication Protocol.

3. Motivation

This section discusses in more detail the motivation and use cases for such an association including but not limited to -

3.1. Opaque Identifier

An opaque identifier may represent attributes such as configured parameters or constraints that a PCEP speaker may invoke on a peer. Thus a PCEP speaker may only need an opaque identifier to invoke these attributes (parameters or constraints).

3.2. Policy based Constraints

In the context of policy-enabled path computation [RFC5394], path computation policies may be applied at both a PCC and a PCE. Consider an Label Switch Router (LSR) with a policy enabled PCC, it receives a service request via signaling, including over a Network-Network Interface (NNI) or User Network Interface (UNI) reference point, or receives a configuration request over a management interface to establish a service. The PCC may also apply user- or service-specific policies to decide how the path selection process should be constrained, that is, which constraints, diversities, optimization criterion, and constraint relaxation strategies should be applied in order for the service LSP(s) to have a likelihood to be successfully established and provide necessary QoS and resilience against network failures. The user- or service-specific policies applied to PCC and are then passed to the PCE along with the Path computation request, in the form of constraints [RFC5394].

PCEP speaker can use the generic mechanism as per [I-D.minei-pce-association-group] to associate a set of LSPs with policy and its resulting path computation constraints. This way simplifying the path computation message exchanges.

3.3. Bundled requests

In some scenarios(e.g.,the topology example described in Section 4.6 of [RFC6805]), there is a need to send multiple requests with the same constraints and attributes to the PCE. Currently these requests are either sent in a separate path computation request (PCReq) messages or bundled together in one (or more) PCReq messages. In either case, the constraints and attributes need to be encoded separately for each request even though they are exactly identical.

If a association is used to identify these constraints and attributes shared by multiple requests, thus simplifying the path computation message exchanges.

4. Overview

As per [I-D.minei-pce-association-group], LSPs are associated with other LSPs with which they interact by adding them to a common association group. This document uses the same association for attributes, called Attribute Association Group (AAG) based on the generic Association object. This document defines a new association type called "Attribute Association Type" of value TBD. An AAG can have one or more LSPs and its associated attributes. The scope and handling of AAG identifier is similar to the generic association identifier defined in [I-D.minei-pce-association-group].

One or more LSP are grouped via a common group identifier in the same way as [I-D.minei-pce-association-group]. The attributes that may be associated with this set of LSPs may either are -

• known to the PCEP peers via some external means like configuration, policy enforcement etc (can be considered as 'out-of-band'). PCEP speaker simply use the AAG identifier in the PCEP message and the peer is supposed to be aware of the associated attributes.
• or communicated to the PCEP peer via PCEP itself on first use (can be considered as 'in-band'). PCEP speaker creates a new AAG by using a new identifier and the associated attributes are communicated via TLVs in association object.

Error handling would be taken up in future revision.

5. Attribute Association Group

The format of the Association object used for AAG is shown in Figure 1:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type   |  Generic flags    |R| Type-specific flags             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             Association group id                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//            Optional TLVs                                    //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   
 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Type=[TBD]          |           Length              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Object-Class  |   OT  |Res|P|I|   Object Length (bytes)       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Object-Class  |   OT  |Res|P|I|   Object Length (bytes)       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                              ...                              ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Object-Class  |   OT  |Res|P|I|   Object Length (bytes)       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    

Xian Zhang
Huawei Technologies
Bantian, Longgang District
Shenzhen  518129
P.R.China

EMail: zhang.xian@huawei.com
             
Udayasree Palle
Huawei Technologies
Leela Palace
Bangalore, Karnataka  560008
INDIA

EMail: udayasree.palle@huawei.com